1. Field of the Invention
The present invention relates generally to three dimensional optical circuits and, more particularly, to a three dimensional optical circuit assembly comprising an optical manifold and a method for making the same.
2. Background of the Invention
Optical fiber networks are becoming increasingly common in modem telecommunications systems, high speed routers, computer systems and other systems for managing large volumes of data. Optical fiber networks typically comprise a large number of optical fibers which are routed over relatively long distances in order to increase transmission speeds and efficiencies relative to the propagation of conventional electrical signals. There is often the need to route individual optical fibers between various connection points throughout a system creating an xe2x80x9coptical circuitxe2x80x9d. One of the more common optical circuits in use today is referred to as an xe2x80x9coptical shufflexe2x80x9d. By way of example only, a simple optical shuffle may be carried out using eight optical fiber cables each having eight individual optical fibers enclosed therein. In what may be referred to as a xe2x80x9cperfect shufflexe2x80x9d, using the fibers of our example here, fiber 1 of each of the eight cables coming in may be routed to a single first cable going out, and the second fiber of each of the eight cables coming in may be routed to a single second cable going out, and so forth. Referring now to FIG. 1, this particular optical shuffle is represented in a simplified schematic in which Cm refers to the input ribbon or cable, CmFn refers to the individual fibers Fn which originate in cable Cm, and Cmxe2x80x2 is the output ribbon or cable following the optical shuffle. It is to be understood, that although this particular example featured only 64 optical fibers, optical circuits often involve a far larger number of fibers which must be routed. Therefore, creating optical shuffles and other optical circuit structures by hand can be a tedious and highly error prone process. One can easily envision the nest of tangled optical fibers occurring in circuits between the input cables and the output cables.
Several solutions have been proposed for the creation of various optical circuits rather than simply trying to route fibers from input points to output points by hand through a large tangle of other fibers. One such solution is the use of semiautomatic machines which weave the individual fibers into the needed circuit arrangement. This solution often requires a significant financial investment in machines which are of little or no use in applications other than the weaving of optical fibers.
Another solution to the problem of creating optical circuits includes a number of attempts to route optical fibers on a flexible polymer substrate. By way of example only, one popular form of this construct is marketed as a Flex Foil(copyright). One such approach to a flexible optical circuit solution is set forth and described in U.S. Pat. No. 5,204,925 issued to Bonanni et al. This reference describes a solution in which a flexible polymer substrate such as Mylar(copyright) or Kapton(copyright) may be coated with a pressure sensitive adhesive (PSA) and have optical fibers mounted thereon. After a number of optical fibers are laid on the substrate in the proper arrangement, a protective cover layer, usually of the same type of material as the substrate, can be bonded on top of the fibers. Of course, the exposed surface of this cover layer may subsequently be coated with an adhesive itself and additional layers of optical fibers and cover materials may be built up in the form of a laminate structure. However, the fiber lay-up process is quite labor intensive and, much like fiber weaving, would require highly specialized equipment to automate. Bonanni et al. further discloses the use of flexible side tabs or thinner strips of substrate material which extend laterally from the main body where the shuffle has occurred, and permit the optical fibers to be bent or rotated at, for example, a 90xc2x0 angle to reorient the fibers from a horizontal position to a vertical position.
Another approach which incorporates a flexible optical circuit is set forth in U.S. Pat. No. 6,005,991 issued to Knasel. This particular reference discloses a printed circuit board (PCB) assembly that includes an interior portion upon which a flexible optical circuit is mounted. Much like the Bonanni et al. reference, Knasel arranges a plurality of optical fibers which are sandwiched between flexible sheets. These flexible sheets are commonly formed of Mylar(copyright) or the like and hold the optical fibers in place and are subsequently bonded to other flexible sheets using pressure sensitive adhesives, as known in the art. In this reference, space is conserved along the edge of a printed circuit board by attaching a multifiber connector to the respective first ends of the optical fibers and using single fiber connectors at the second ends of the optical fibers where space is more readily available, such as the less populated interior portion of the printed circuit board.
It should also be noted that both of these flexible circuit approaches are generally implemented in the form of large sheets with prerouted fiber networks or printed circuit boards with flexible optical circuit portions mounted thereon. In either case, these circuits normally have splices at both the input and output ends of the optical circuit to facilitate attachment to the input fiber cables and the output fiber cables during installation. Splices are normally required to overcome the length limitations of the tabs extending from the body of the flexible circuit. Additionally, splices may be used to attach specialized connectors to the input and output ends of the circuit for coupling to ruggedized cables. The splices at both the input and output end of the shuffle or optical circuit produce optical signal losses which when added across an entire optical network may be significant and unacceptable to the user. Furthermore, both mechanical and fusion splices commonly require considerable amounts of space because of the need to mechanically reinforce or strengthen the splice. Additionally, the flexible optical circuit approaches described here generally do not permit the use of protectively sheathed or xe2x80x9cruggedizedxe2x80x9d fiber optic ribbons leading all the way up to the flexible circuit, nor do they offer much protection to the optical fibers within the circuit or shuffle beyond the meager protection provided by a single layer of polymer film. Moreover, flexible optical circuit designs do not isolate and protect the individual fibers in that, at crossing points within the circuit, many of these fibers are in direct contact with each other.
Therefore, there is a need for three dimensional optical circuits which can be created without the expense of weaving machines and which can be more readily routed into a number of different shuffle arrangements. There is a need for an optical circuit arrangement which is less labor intensive than building up a multilayer laminate structure of Mylar(copyright) film, pressure sensitive adhesive and optical fiber, several strands of optical fiber at a time. There is also a need for an optical circuit which allows ruggedized ribbons of fiber optic cable to be run up to the circuit and away from the circuit and which provides a ruggedized protected environment for the optical fibers during the shuffle itself. There is a need for a three dimensional optical circuit having fewer fiber splices and reduced optical signal loss. Additionally, there is a need for a three dimensional optical circuit which fits into environments with limited surface area (x-y axes) by more efficiently stacking the shuffle to fully utilize space in a vertical direction (z-axis).
The three dimensional optical fiber circuit apparatus and method described herein below will address each of these aforementioned needs and provide a number of additional benefits as well. In one embodiment, the present invention is a rigid, unitary, three dimensional manifold constructed using a rapid prototyping process such as, but not limited to, stereolithography (xe2x80x9cSLAxe2x80x9d), fused deposition modeling (xe2x80x9cFDMxe2x80x9d), selective laser sintering (xe2x80x9cSLSxe2x80x9d), and the like. Note that the terms rapid prototyping and rapid manufacturing are interchangeable in regard to the present invention in that this technology may be utilized not only for creating prototypes, but actual manufacturing as well.
Although the equipment for carrying out SLA processes and other rapid prototyping techniques are relatively expensive machines, these systems are general purpose and are readily available. SLA machines and other rapid prototyping machines are readily programmable to create virtually any three dimensional object which can be designed on a computer aided design (xe2x80x9cCADxe2x80x9d) system. Accordingly, the design of a three dimensional manifold for routing a large number of optical fibers may be laid out in any number of configurations or arrangements limited only to the capabilities of the CAD system or the imagination of the designer. Moreover, it is possible to program these systems to create passageways or channels for routing optical fibers to provide for an appropriate bend radius and thereby minimize optical signal loss, and to isolate and protect the individual fibers throughout the optical circuit. Further, it is possible to create optical circuits that could not be readily manufactured using conventional molding or forming techniques.
The fiber optic manifold, in accordance with the present invention, may take any number of possible embodiments, including a solid block having a number of hollow passageways connecting input points and output points or a large plurality of rigid hollow tubes which again have a number of input points and output points. By way of example only, these input openings may be arranged in a matrix having an equal number of rows and columns. In the case of 8 fiber optic cables each having 8 fibers, this would require an optical manifold having 64 input openings, 64 output openings, and 64 passageways connecting therebetween. If the input and output ends of the manifold are properly labeled, it should be relatively easy for a user to determine which optical fiber is to be inserted into the appropriate opening and will be exit from the appropriate opening on the opposite end of the manifold. Moreover, since there is only one passageway connecting a particular input with a particular output there is no need to worry about fibers becoming entangled within each other or causing confusion for the person guiding them through the manifold.
In yet another embodiment, the present invention is a process for forming a three dimensional optical circuit including the steps of providing a rigid, unitary optical manifold having an input end and an output end; arranging a plurality of optical fiber cables leading up to the input end of the manifold, and arranging a plurality of optical fiber cables leading away from the output end of the manifold; splitting out the individual fibers of each input cable and guiding each fiber to an individual input opening of the manifold, collecting up the individual fibers extending from the output openings of the optical manifold and gathering them back up into optical cable bundles. Generally, it is possible to merely strip and separate the optical fibers from the input cables and feed them into the input openings of the manifold, passing them through the manifold and then terminating the resulting cable groups at the output side only and have no fiber splices within the shuffle itself. Thus, it is not unreasonable to completely eliminate optical signal losses incurred by splices within individual optical circuits, including shuffles. This reduction in optical signal losses could be quite significant if multiplied throughout an entire optical network.